A modular zoom reimager which includes an interchangeable compensator/ocular unit is disclosed in the paper of A. Mann entitled "Infrared zoom lenses in the 1980s and beyond" published in Optical Engineering, 31 (5), pages 1064 to 1071 (May 1992).
U.S. Pat. No. 5,044,706 discloses a telescope (Galilei, afocal) having a focal length (field of view) which can be changed by insertable lens groups. Diffractive optical elements and aspheric elements are provided in the additional lenses and in the base objective.
U.S. Pat. No. 5,214,532 discloses an achromatic two-lens accessory for thermal imaging apparatus to double the range. Aspheric lens elements are provided.
U.S. Pat. No. 5,229,880 discloses a reimager which is configured for three fields of view by omitting or inserting a first or second two-lens group behind the front lens of the objective. In the embodiments shown, this two-lens group has at least one diffractive optical element. Claim 9 of this patent, however, presents an embodiment without a diffractive optical element.
U.S. Pat. No. 5,257,133 describes a reimager having a diffractive optical element in the ocular as set forth in claim 1 or no diffractive optical element as set forth in claim 10. The use of aspheric lenses in the objective and ocular is shown and these aspheric lenses are made of silicon, that is, for a 3 to 5 .mu.m wavelength. An interchangeable optic is not provided.
U.S. Pat. No. 5,363,235 discloses a catadioptric reimager having interchangeable lenses for switching the image field.